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How To Clear A Blocked Waste Pipe

If you need to clear a blocked waste pipe, this guide will help.  We have provided a variety of methods to clear a blocked waste pipe.  Every home relies on an effective drainage system to ensure waste drains away from the house properly.  No matter how big your blockage, it should be dealt with immediately.  After the blockage has been removed, you should think about why it blocked in the first place.  Knowing how your drainage system should work can help you think of preventative measures.

Types of Household Waste Pipe

In general, household waste pipes come in three different sizes in the UK.  32mm for hand basins and 40mm for showers, washing machines, sinks and baths.  Toilets usually have a 110mm pipe.  Every waste pipe in your home must slope downwards at a rate of at least 20mm per metre, this is to ensure the water flows properly.

Types of Household Waste Trap

Waste traps come in 3 different designs such as a bottle, P or S waste traps.  Bottle and P traps are the most common types in the UK.  Current plumbing regulations do not recommend S traps because water can be easily siphoned from the trap, therefore preventing a seal from gases.

Waste traps are designed to prevent smells coming back up your waste water pipes.  All waste traps are designed to trap water. The water sits in the waste trap bend, creating a gas barrier.  When running the tap, water is pushed out of the bend and replaced with new water.  It is essential that waste traps are cleaned out now and again, as these are the places where hairs and fats are likely to accumulate first.  A poorly designed waste trap can increase your chances of a blockage.  For example, a poorly designed bottle waste trap may have a narrow passage for water to flow.  Such a waste trap will collect debris such as hairs or food more easily, thus increasing the chances of a blockage.  We only recommend waste traps manufactured by McAlpine, as they seem to have the best designs.

P Type Waste Trap

The P type waste trap below is ideal for sinks which require two waste inlets.  It can also accept discharge from a washing machine or dishwasher via its horizontal nozzle.

Buy this McAlpine waste trap from the Amazon store

Bottle Type Waste Trap

The bottle trap below is ideal for sinks that have limited space beneath.  You can also get McAlpine bottle traps which has a horozontal nozzle for dishwasher or washing machine discharge.

Buy this McAlpine bottle waste trap from the Amazon store

Unblocking Tools Needed

Pipe Cleaning Brushes

Buy these tube cleaning brushes from the Amazon store

clear a blocked waste pipe

Drain Unblocking Chemicals

It is best to use a checmical drain cleaner that does not damage your plastic pipes, or the joins between them.  Chemical drain cleaners can be very effective, and also help to reduce bad odurs from your pipes.

Buy this HG drain unblocker from the Amazon store

clear a blocked waste pipe


Buy this plunger from the Amazon store

How Clear a Blocked Kitchen Waste Pipe

Kitchen sink blockages are usually a result of oil and fats being poured down the sink.  These fats and oils can harden over time inside your waste pipes.  Once they start to solidify, waste food particles then start to accumulate.

Another problem some people experience with kitchen sinks are issues related to washing machine or dishwasher waste.  This is because these appliances usually share the same drain as a kitchen sink.  Waste from a dishwasher can be particularly problematic, as dishwasher soap can harden and buildup in pipes.

A clogged kitchen waste pipe can to be tackled in a number of ways, we have listed the 3 most popular methods below.

You will notice that the plunger method has not been mentioned for unblocking kitchen sinks.  This is because it is not that effective at unclogging blockages caused by fats and oils.  After the blockage has been cleared, you may want to consider flushing your pipes through thoroughly with boiling water once a month.  Boiling water helps to break down any fats that could be building up.

  1. Clean or Replace the Waste Trap.
  2. Dismantle and Clean your Kitchen Waste Pipes.
  3. Use Chemical Drain Cleaner.

How to Clear a Blocked Basin Waste Pipe

Unlike kitchen sink waste pipes, blocked basin pipes are probably not due to fats and oil buildup.  The most likely culpit is probably hair.  This is because bathroom sink basins often have a pop up type of plug, which easily traps hair.  Bathroom sinks are also rarely filled up and emptied, meaning they rarely get a good flush through.

Soap and other products washed down bathroom basins can also build up slowly in the pipe work.  Over time the build up of these deposits reduce the flow of water, or even stopping it completely.

Below are some of the things you could try to unblock a basin waste pipe:

  1. It is always worth trying a plunger first. Make sure you cover any overflow spouts before you begin plunging so you can get a strong seal.  Pressure caused by the plunger can help loosen any blockages.  Plungers are very useful for solid blockages.
  2. If you have a pop up basin plug, try removing and cleaning it.  You will be surprised how much hair can build up around these plugs.  Your pop up plug is most likely held in place with a nut attached to the drain just under the sink. Reach behind the drain pipe under the sink to find the pop-up nut.  Remove the pop up plug and give it a thorough clean before putting it back.  how to clear a blocked waste pipe
  3. If the methods above do not work, you will probably need to dismantle the pipe work under your basin, and give it a thorough clean.


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Posted on 25th March 2019 at 4:37 pm


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